This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Phosphorylation is one of the most frequent posttranslational modifications of proteins. In a cell, about 30% of the total proteins are phosphorylated to some extent. Protein phosphorlyation-dephosphorylation events play a primary role in almost all aspects of cell function including signal transduction, cell cycle or apoptosis. The activation of the immune response mediated by T lymphocytes is dependent on protein phosphorylation-dephosphorylation events. In order to understand the functionality of lymphocytes in an immune response we need to study the phosphorylation profiles that occur in these cells in response to activation. Considering the complexity of a whole cell lysate and the low amount of phosphorylated peptides versus the non-phosphorylated ones, a robust and effective method for the analysis of the phosphoproteome is of the highest importance in the field of proteomics. Mass spectrometry will be used to identify different posttranslational modifications, such as phosphorylation and their site assignment in human primary T cells. Quantitative methods, such as iTRAQ, will be used to determine the dynamics of the phosphorylation state.